1. Field
This application relates to roofing materials, and more particularly to roofing materials having tailored radiation properties and tailored aesthetic properties in separate directions, simultaneously.
2. Prior Art
Roofing
Several types of roofing material are commercially available including asphalt shingles, wood shingles, metal roofing, slate, clay tiles, built-up roofs, roll roofing, polyurethane foam, single-ply roof membranes and others. Asphalt shingles are by far the most commonly used in the U.S. for residential sloped-roof applications. Asphalt shingles are constructed of a felt or fiberglass mat that is saturated with asphalt and covered with granules which are adhered to the mat. Advantages of this type of roofing include its low cost, durability, aesthetic variety (colors, shading, layers and textures), as well as ease of installation and repair. The granules of asphalt shingles are generally derived from a hard mineral base rock such as slate, basalt or nephelite, and are typically ground to a particle size of about 10 to 35 US mesh. Granules are typically coated prior to being applied to shingles to achieve a variety of desired properties. This has been done for many years as illustrated by U.S. Pat. No. 2,379,358 (1945) to Jewett.
Aesthetic Properties
The aesthetic properties of roofing systems play a primary role in marketing. As a result, asphalt shingles are often tailored to achieve certain appearances. This tailoring is typically accomplished through uniform granule coating and by applying a mixture of granules in various color schemes and patterns and/or layering shingles to simulate more traditional, and in most cases more expensive, forms of roof coverings such as wooden shakes, slate or tile. Examples of these methods are described in U.S. Pat. Nos. 7,665,261 (2010) to Elliott et al., 6,289,648 (2001) to Freshwater et al. and 6,014,847 (2000) to Phillips with the layering approach emphasized in U.S. Patent Application Publications 2010/0205898 and 2010/0192501 and U.S. Pat. No. 6,698,151 (2004) to Elliott. U.S. Pat. Nos. 6,715,252 (2004) and 6,523,316 (2003), both to Stahl et al., describe the combination of coloring and layering with colors changing at edges facing specific directions to achieve a sharp, precise delineation between zones of different shadings in an interesting effort to simulate the depth of more expensive shingles. U.S. Pat. Nos. 7,638,164 (2009) to Aschenbeck and 4,583,486 (1986) to Miller describe methods for accurate granule placement in complex patterns to achieve desired aesthetics. Darker and multi-toned shingles remain preferred in the market place. The visual appearance of a material is strongly influenced by the surface properties, including color, tone, reflectivity, and surface irregularities and their orientation. The resulting properties of all tailoring for visual effect, is referred to herein as “tailored aesthetic properties.”
The effective directional dependence of appearance is strongly influenced by surface properties and orientation. Methods described in the prior art to improve the visual appearance do so with large-scale efforts apparently without considering that these properties can be tailored to have directional preference at the granule level.
Roof Temperatures
While the aesthetics of a roofing system remain of primary marketing importance, effective service life has always been important and energy considerations are becoming increasingly important in the selection of roofing materials. In particular, roofs that reflect large amounts of solar radiation are becoming favored because they reduce the temperature of the shingles thereby extending the service life of the shingles and reducing the cooling loads for the building. In addition, as described in U.S. Pat. No. 7,648,755 (2010) to Gross et al., hotter roofs in metropolitan areas can result in a “heat island effect” causing ambient air temperatures to be as much as 10° F. higher than in surrounding rural areas.
Radiation Properties
As described in U.S. Pat. No. 7,592,066 (2009) to Shiao et al., conventional asphalt shingles are known to have low heat reflectance in the spectral band associated with solar radiation. This spectral band is predominantly in the near infrared range (700 nm to 2500 nm). As a result, conventional asphalt shingles absorb a large portion of incident solar radiation. This low solar reflectance can be exacerbated with dark coloring of the granules. The patent of Shiao et al. indicates that dark colored asphalt shingles have solar reflectances of only 0.05 to 0.15. The heat absorbing properties of conventional shingles result in elevated roof temperatures that adversely affect shingle service life and cooling requirements. Special treatments can be incorporated to increase the reflectivity of asphalt shingles. These treatments can be applied specifically to the granules or to the entire shingle. The thermal response of a material to incident radiation such as solar radiation is determined by the surface radiation properties. These include the reflectivity, absorptivity, transmissivity and emissivity. Methods described in the prior art to improve the thermal response to solar incidence do so by incorporating features that effect the surface radiation properties. In particular, treatments that increase the surface reflectivity are commonly used. The resulting properties of any such tailoring, including the use of reflective granules, coatings, paints, powders or other means designed to alter the radiation properties in order to improve thermal performance is referred to here as “tailored radiation properties.”
The effective directional dependence of reflectivity is strongly influenced by surface properties and orientation. Methods described in the prior art to improve the radiation properties do so with large-scale efforts apparently without considering that these properties can be tailored to have directional preference at the granule level.
Granule Reflectivity
Effective methods for obtaining highly reflective granules have been pursued for many years as illustrated by U.S. Pat. No. 2,732,311 (1956) to Hartwright. Modern efforts have focused on balancing the desire for high reflectivity with that for darker tones. This results in compromising both areas of interest. Many schemes have been developed to accomplish this balance as demonstrated in U.S. Patent Application Publications 2010/0203336, 2010/0151199, 2010/0104857, 2008/0241472 and 2008/0008832 as well as U.S. Pat. Nos. 7,648,755 (2010) to Gross et al. and 7,241,500 (2007) to Shiao et al. These include solar reflective particles dispersed in a binder at a desired depth, coated reflective granules, reflective coatings, multiple coatings, colored particles within a coating and reflective particles within a colored coating. Regardless of these efforts the most reflective roofs commercially prevalent are light in color.
Granule Alternatives
Instead of treating granules to increase their reflectivity, the granules can be replaced with a more reflective material such as the metal flakes described in U.S. Patent Application Publication 2009/0117329. This method can result in improved reflectivity, but requires deviation from the established, efficient and low-cost process of producing rock-based granule-coated shingles. In addition, this method does not take advantage of the extensive availability of aesthetic choices for typical granule-based shingles.
Shingle Treatments
Methods have been developed to increase average resulting shingle reflectivity by applying a layer of reflective material to the surface of the shingle. This reflective layer can be in the form of a paint as in U.S. Patent Application Publication 2009/0317593, U.S. Pat. No. 7,291,358 (2007) to Fensel et al. and U.S. Patent Application Publication 2007/0110961 or a powder as in U.S. Pat. Nos. 7,452,598 (2008) to Shiao et al. and 7,422,989 (2008) to Kalkanoglu et al. This is most effective with the use of highly reflective materials that are generally light in color and these methods produce roofs that are light colored in appearance regardless of the direction from which they are viewed.
U.S. Pat. Nos. 7,291,358 (2007) and 6,933,007 (2005), both to Fensel et al., and U.S. Patent Application Publications 2005/0238848, 2007/0110961 and 2009/0317593 describe the use of two sizes of granules to increase granule coverage. The smaller granules are sized to fit in the interstices between the larger granules thereby reducing the amount of non-reflective asphalt material exposed to solar radiation. This can increase the average resulting shingle reflectance since granules are typically more reflective than the black asphalt substrate. This is most effective with the use of highly reflective granules that are generally light in color. These methods produce roofs that are light colored in appearance regardless of the direction from which they are viewed.
Shaped Shingles
Popular shingle materials have a variety of shapes. Wood shake shingles are very thin at the uppermost end tapering to considerably thicker at the lower, exposed end. Tile shingles have a variety of curved or flat shapes with interlocking features at interfaces designed to prevent water penetration of the shingle system. While there is a variety of shapes of popular shingles, none of the current art designs capitalize on shape to accomplish directional properties. More particularly, there have been no attempts to create shingles with large scale surfaces that face the sun direction and others that face the viewing directions to facilitate directional tailoring for desired properties.